Dynabeads - Anyone use them?

[Scissors]

Lets hear them. Either they work, or my SMT has perfectly balanced rims and tires out of the box.

The laws of physics, for one.  And rims and tires don't have to be perfectly balanced in order to feel balanced.  Most automotive (and bike) suspension systems have a natural resonance frequency which coincides with a specific rotational speed (usually anywhere from 50-80 MPH, depending upon a number of factors.)  Meaning you won't necessarily feel it as being out of balance at lower or higher speeds.

One reason they don't work is simple momentum.  Any time you change the rotational speed of your wheel, Newton's first law kicks in.  Meaning anything within the tire will attempt to continue going the direction and speed it was already traveling.  Assuming that they were in a position so as to balance the wheel at a steady speed, upon deceleration the beads/dust/water/whatever you have in there will continue in the direction of rotation until friction slows them down to the wheel's speed.  Conversely, any time you accelerate, they will shift backward in relation to the tire until friction speeds them up to the wheel's speed.

This isn't a problem for traditional weights as they're fixed to the wheel.  And unlike weights, they can't address lateral imbalances at all.

If they did work, and that's a big "if", you could get literally the same effect by putting a fluid in your tires.  Plus, if you have an imbalance greater than the total mass of the dynabeads, they still couldn't work even if they did magically stay on the exact opposite side from it.

To avoid typing everything all over again, here's my post from another forum:

First off, what happens when you change the rotational velocity of a tire which contains anything not attached to the tire? That's right, the object(s) maintain their momentum--Newton's first law. For the same of keeping typing easier, we'll refer to the wheel/tire combo as simply "the wheel".

Say you have a wheel that is out of balance. We'll call the heavy point "angle 0" and say that it's 1 gram and 8 inches from the axis of rotation. Now if dynabeads were to work, they would need to be exactly one gram, and would need to sit directly across from the heavy point, at 180 degrees away, and at the same distance from the axis of rotation. Say they actually do this, and sit at this point with that mass while the wheel is rotating at, say, 200 RPMs: what happens when you change the wheel's angular velocity? That's right, things inside the wheel move in relation to the wheel. If the wheel decelerates, things inside of it will move in the direction of rotation until friction and other losses reduce their velocity. During this period, the wheel will be out of balance. The same goes for acceleration of the wheel, in which case the contents, such as beads, will go backward in relation to the wheel, again putting it out of balance. So every time you change your speed, your wheels are going out of balance.

Secondly, centripetal force. While rotating, any mass within the wheel won't gravitate toward the lightest point but, rather, will try to continue along a straight path in the direction that it is alreadly traveling. However, the tire prevents the beads from doing this and holds them back. Because of this, they will tend toward the point furthest from the axis of rotation, not the point of least mass.

Thirdly, mass versus distance. Any mass further from the axis of rotation will have more of an effect on balance than an equal mass closer to the axis. Well dynabeads can't magically create mass from nothing. So what if you need more mass to balance your wheel than you added in dyna beads? At best, they'll sit at the outer part of the inner surface of the tire. If there isn't enough mass, they simply can't work any more than a perpetual motion machine could. If there's too much mass in dynabeads, where does the excess go? The same supposed force that causes bead #1 to go where it needs to would also cause bead #300 to go to the same place. The only thing stopping them is that they can't occupy the same space, and therefore they would clump.

So why does it seem to work for some people? Simple. Most wheel/tire combinations aren't far enough out of balance for a rider/driver to notice. You can put absolutely nothing on them and they'll seem to be fine. If dynabeads worked, so would oil. You could literally put an equivalent mass of oil in your tire and it would do the same thing for cheaper.

[Triple J]

I'm not convinced they don't work.

I agree with your argument that fluid would also work. The principles are the same.

Also agreed that you need enough bead mass to make a difference, just like you need enough weight mass. However, you need less bead mass since the beads are further away from the center of rotation. Too much bead mass isn't an issue because the extra disribute themselves evenly after a balanced condition is achieved. This can be easily demonstrated by putting bbs or a fluid in a round container and spinning it...they will orient themselves fairly evenly around the perimeter and not clump...provided the container is round and the rotation point is centered.

I also agree that the beads (or fluid) will change position on acceleration or deceleration. However, it is irrelevant. Out of balance wheels are felt at a constant speed when the frequencies align, not during changes in speed. At contant speed, the beads position themselves due to the combination of forces holding them in place against the tire. The tire being out of balance while the beads reposition is true, but it doesn't matter as it can't be felt anyway. As an example, my Xterra wheels lost some weights over the winter. I only felt the out of balance condition between 55-60 mph...everything was fine otherwise even though the wheel was still out of balance. New weights fixed the problem.

Your argument about beads clumping at the spot which is furthest from the center of rotation, while true in general, is again irrelevant in this case. Tires are round, so the beads are always equal distance from the axle. If the tire wasn't round there wouldn't be any way to get a smooth ride period.

Your point about lateral balancing is also true. The problem is lead weights on moto tires don't usually address it either since most balancing is done on a static balancer which can't account for lateral balancing. Most of the time lead weights are just put close to the center of the rim...or split 1/2 inside and 1/2 outside to try not to induce any lateral imbalance. I don't think lateral imbalance is a real issue with moto wheels.

The principal should be able to be proven, or disproven, by a simple experiment. The question as to whether modern motorcycle rims/tires even need balancing is a good one, and makes proof by example a bit more difficult...my SMT wheels may very well not need balancing. Of course, using your theories, wouldn't the beads in them now throw them out of balance though due to clumping?




 

[VisceralReaction]

From a mechanical engineer:

First I want to frame the question.  Wide low profile tires and wheels entail three dimensional complications which we should leave out.  Also, the beads are recognized as not solving "lateral imbalance".
Also I think we should exclude out-of-round tires.

So, if a tire is geometrically circular and properly centered in its axle but is out of balance so that a segment has greater mass than other geometrically equal segments, do the beads self-locate so as to correct the imbalance?

Yes.

The beads feel the so-called centrifugal force in the rotating tire and, if they can, they will role to the place farthest from the Axis of rotation (like rolling downhill).  We have said, however, that the tire is properly round and centered, so, at first glance, we can see no preferred collection point for the beads.  Each spot around the tire is equidistant from the axle.

Now, if the axle was hard fixed in a bearing with no chance of movement that would end the discussion.  The bearing would be forced to handle the imbalance and the beads would do nothing significant.

But our vehicle has a suspension system and the axle moves as required.  As the vehicle speeds up, the force of the imbalance increases.  This is the tire's increasing preference to rotate around its own centre of mass, and, because the tire is out of balance, its centre of mass is not exactly at the centre of the axle.

At sufficiently high speed, the axis of rotation moves away from the axle centre towards the centre of the rotating mass.

Obviously, the centre of mass is on the heavy side of the wheel with respect to the centre of the axle.

So we have our whole wheel and tire rotating around a spot that is slightly off the axle centre, and the part that is farthest away from the new axis of rotation  is on the opposite side from the overweight sector.  But this is precisely where the beads will roll...  to the spot farthest from the axis of rotation.

To repeat: it is because the centre of mass becomes the axis of rotation that the points around the tire are no longer equidistant from the axis of rotation.

[chris1044]

If they did work, and that's a big "if", you could get literally the same effect by putting a fluid in your tires.  Plus, if you have an imbalance greater than the total mass of the dynabeads, they still couldn't work even if they did magically stay on the exact opposite side from it.

I don't have time to go into mathmatical calculations, but they do work to reduce the RADIAL imbalance on tires.  They will have ZERO effect on dynamic balance. 

What VisceralReaction posted is basically what I was going to say....you can do the math and see they will reduce radial imbalance.  Anyone claiming this doesn't work needs to go have a chat with a over-the-road truck driver.  Semi tires have been running Equall (powder form of this) for decades.  Be skeptical all you want, they work.

[ducatiz]

should be a very simple issue.  put them in a new tire and run them on a balancing machine.

[Triple J]

should be a very simple issue.  put them in a new tire and run them on a balancing machine.

Read Visceral's post. A balancing machine leaves out the suspension action, which is critical.

[scott_araujo]

After watching the video I believe they work but I was wondering if the suspension comes into play.  On a bike the tires get bounced around more than a car.  Would this knock the beads out of place?  Seems people who are using them here don't notice that happening.

Scott

[ducatiz]

Read Visceral's post. A balancing machine leaves out the suspension action, which is critical.

Yes, but it would at least show whether or not they are doing anything at all.  Wheels are not balanced on a suspension, they are balanced on a fixed axle.  If the beads will balance a tire on a fixed axle then they do have SOME value.

[Triple J]

Yes, but it would at least show whether or not they are doing anything at all.  Wheels are not balanced on a suspension, they are balanced on a fixed axle.  If the beads will balance a tire on a fixed axle then they do have SOME value.

Wheels with weights are balanced on a fixed axle, not those using the beads. If the suspension action is required to allow the beads to orient correctly, then testing them on a balancing machine with a fixed axle is useless.

[ducatiz]

Wheels with weights are balanced on a fixed axle, not those using the beads. If the suspension action is required to allow the beads to orient correctly, then testing them on a balancing machine with a fixed axle is useless.

My point was to compare apples to apples.  I.e. "how does a tire with beads behave on a traditional balancing machine?"

if i put it on the machine and it's balanced, then that's good enough for me.  my car tires are balanced on a fixed axle but on the car they bounce all over the place.

[duc_fan]

The laws of physics, for one.  And rims and tires don't have to be perfectly balanced in order to feel balanced.  Most automotive (and bike) suspension systems have a natural resonance frequency which coincides with a specific rotational speed (usually anywhere from 50-80 MPH, depending upon a number of factors.)  Meaning you won't necessarily feel it as being out of balance at lower or higher speeds.

One reason they don't work is simple momentum.  Any time you change the rotational speed of your wheel, Newton's first law kicks in.  Meaning anything within the tire will attempt to continue going the direction and speed it was already traveling.  Assuming that they were in a position so as to balance the wheel at a steady speed, upon deceleration the beads/dust/water/whatever you have in there will continue in the direction of rotation until friction slows them down to the wheel's speed.  Conversely, any time you accelerate, they will shift backward in relation to the tire until friction speeds them up to the wheel's speed.

This isn't a problem for traditional weights as they're fixed to the wheel.  And unlike weights, they can't address lateral imbalances at all.

If they did work, and that's a big "if", you could get literally the same effect by putting a fluid in your tires.  Plus, if you have an imbalance greater than the total mass of the dynabeads, they still couldn't work even if they did magically stay on the exact opposite side from it.

To avoid typing everything all over again, here's my post from another forum:

Dewd... half of your argument (the post on the other forum) is cut to shreds by the simple demonstration video on the first page of this thread.  The balancing agent DOES move toward the side opposite the heavy part of the rim.  One test is worth more than a thousand "expert opinions".

As far as the acceleration/deceleration, I would agree... but only in extreme cases like track use: wide open throttle alternating with maximum braking.  The rest of the time, friction will keep them in place ENOUGH that the tires don't feel out of balance.  As demonstrated by multiple members here, they don't appear to make things worse when accelerating/decelerating in street use.  Again, one test is worth more than a thousand opinions... and we have more than one real-world test in this thread alone.

If I ever have an unsolvable wheel balance problem, I'll give them a try.  They have worked in real-world trials.  Right now I have no such problem, and hence no need for them.  We'll see what happens in a few thousand miles when my tires need changed.

[VisceralReaction]

Tiz,
you are comparing apples to oranges though.
You are comparing static vs dynamic balancing agents.
Static being lead weights, they sit on the rim and balance the wheel, whether on a fixed axle
or a suspended axle.
Dynamic being the beads, because the can move within the tire carcass. On a fixed axle they will
do nothing. The suspension movement allows the beads to distribute away from the heavy
side of the tire, the beads don't work without suspension.

[Greg]

If I ever have an unsolvable wheel balance problem, I'll give them a try.  They have worked in real-world trials.  Right now I have no such problem, and hence no need for them.  We'll see what happens in a few thousand miles when my tires need changed.

I used them because I bought my own tire changer and didn't want to static balance the tires. After using the beads I am completely sold on them, and the ride is now so smooth it's almost weird. I've had plenty of tires put on before at a shop, and while they always felt pretty good, I always put any slight vibration down to road surface irregularites, even when riding on very smooth road. Sometimes you might think you know what a balanced wheel feels like, but until you've tried one that feels perfect, you don't know what you're missing.

[ducatiz]

Tiz,
you are comparing apples to oranges though.
You are comparing static vs dynamic balancing agents.
Static being lead weights, they sit on the rim and balance the wheel, whether on a fixed axle
or a suspended axle.
Dynamic being the beads, because the can move within the tire carcass. On a fixed axle they will
do nothing. The suspension movement allows the beads to distribute away from the heavy
side of the tire, the beads don't work without suspension.

I'm not comparing the agents.  I am comparing the outcome.  If both yield a balanced wheel, then who gives a damn if the agent is static, dynamic or fairy dust?

[Greg]

When you use weights, you are balancing the wheel, and assuming the tire doesn't change. We all know tires flex thereby changing the overall relationship, plus tires do not wear evenly. The beads constantly adjust, but the weight stays static.

All I can say is try them and you'll become a believer, like I did.